The invention relates generally to syringes and more specifically to pre-tipped syringes utilized to dispense an amount of fluid to a surface.
In various types of medical and dental procedures it is often necessary for an individual to dispense an amount of a fluid onto a surface being treated. The fluids can have various purposes, such as to sterilize, anesthetize, etch, bond, clean or treat in some manner the surface being examined during the procedure.
In order to precisely deliver the fluids onto the surface for the desired purpose, a number of different delivery systems have been developed. One such delivery system is a syringe and application tip. The syringe is formed with a barrel containing an amount of the fluid to be dispensed and a nozzle at one end of the barrel from which the fluid is expelled from the barrel, most commonly the nozzle is a standard luer taper to accept luer tapered application tips. Opposite the nozzle, a plunger is slidably positioned within the barrel and includes a bung that contacts the fluid within the barrel. The plunger can be moved within the barrel in order to compress the fluid via the bung to urge or force the fluid from within the barrel out of the syringe through the nozzle and subsequently through the application tip. The amount of fluid dispensed from the nozzle is controlled by the force applied to the fluid via the plunger and the back pressure developed due to the application tip constrictor diameter, and thus the individual can determine the amount of fluid to be dispensed or the rate at which the fluid is dispensed.
However, with syringes of this type, one significant issue is the inability to immediately stop fluid being dispensed from the syringe once positive pressure has been removed from a user. More specifically, when the pressure being applied to the fluid via the plunger is removed, residual pressure remaining in the fluid within the barrel causes an amount of the fluid to be dispensed, or to drip from the nozzle and/or application tip, even when no pressure is actively being applied to the fluid. As the inadvertent dispensing of the fluid can have highly undesirable consequences, depending on the nature of the fluid and/or the cost of the fluid, among other issues, it is highly desirable to prevent any dripping of the fluid from the syringe. One example of accidental spillage or dripping common to dentistry is the inadvertent spillage of sodium hypochlorite during endodontic procedures. Accidental spillage of sodium hypochlorite is probably the most common accident to occur during root canal irrigation. Even spillage of minute quantities of this agent on clothing will lead to rapid, irreparable bleaching. The patient should wear protective coverings and eyewear, and the practitioner should exercise care when transferring syringes filled with hypochlorite to the oral cavity. Additionally, seemingly mild burns with an alkali such as sodium hypochlorite can result in significant eye injury as the alkali reacts with the lipid in the corneal epithelial cells, forming a soap bubble that penetrates the corneal stroma. The alkali moves rapidly to the anterior eye chamber, making repair difficult. Further degeneration of the tissues within the anterior eye chamber results in perforation, with endophthalmitis and subsequent loss of the eye [Spencer H R, Ike V, Brennan P A. Review: the use of sodium hypochlorite in endodontics—potential complications and their management. Br Dent J. 2007 May 12; 202(9):555-559.].
Ingram recorded a case of accidental spillage of 5.25% sodium hypochlorite into a patient's eye during endodontic therapy [Ingram T A. Response of the human to accidental exposure to sodium hypochlorite. J Endod 1990; 16: 235-237]. The immediate symptoms included instant severe pain and intense burning, profuse watering (epiphora) and erythema. Loss of epithelial cells in the outer corneal layer may occur. There may be blurring of vision and patchy colouration of the cornea [Gatot A. Arbelle J. Leiberman A et al. Effects of Sodium hypochlorite on soft tissues after its inadvertent injection beyond the root apex. J Endod 1991: 17: 573-574]. Immediate ocular irrigation with a large amount of water or sterile saline is required followed by an urgent referral to an ophthalmologist. Similar complications can occur when sodium hypochlorite accidental drippage or spillage occurs to skin or oral tissues during root canal therapy. As such, an anti-drip syringe and application tip system would be highly advantageous for dental and medical procedures to prevent accidents and patient harm.
In certain prior art solutions to this issue, a number of different types of syringes have been developed in an attempt to counteract latent pressure within the device. One such syringe is disclosed in U.S. Pat. No. 4,678,107, entitled Dripless Dispenser For Liquid And Viscous Fluids, which is expressly incorporated herein by reference for all purposes. In this syringe, a cap having a concave surface is disposed on the end of the plunger disposed within the barrel of the syringe. The concave surface is flattened by a plate on the end of the plunger when pressure is applied to the fluid via the plunger to dispense fluid from the syringe. When the force exerted on the plunger is removed, thereby disengaging the plate from the cap, the cap returns to its concave shape to apply a negative pressure or vacuum on the fluid within the barrel and nozzle, thereby preventing the fluid from dripping out of the nozzle.
However, while the cap includes a pair of sealing rings engaging the cap with the interior surface of the barrel to provide a fluid seal between the cap and the barrel, when the cap is in the concave position there is no support provided to the cap at the sealing rings. Thus, due to the inherent flexibility of the material forming the cap and sealing rings, the sealing rings can become separated from the interior surface of the barrel when the plunger is not actively being pressed against the cap. As a result, the fluid held within the barrel can leak around the cap and out of the barrel around the plunger, which is highly undesirable. As such, the syringe and bung design disclosed in U.S. Pat. No. 4,678,107 would have limited applications for use (i.e. viscous fluids and/or low positive pressures/exertion forces) in order to prevent leakage around the bung during use. In addition to the syringe disclosed in the '107 patent, other prior art dripless syringe designs, such as those disclosed in U.S. Pat. Nos. 4,708,270 and 6,796,217, also include caps or bungs that can deform within the barrel in a manner that comprises the fluid seal between the cap or bung and the barrel.
Endodontic therapy, by virtue of the root canal geometry, requires small gauge needle tips during irrigation. Unfortunately, as described by Gopikrishna et al., needle gauge lumen diameter has a negative impact on therapeutic irrigant flow rates [Gopikrishna V, Sibi S, Archana D, Pradeep Kumar A R, Narayanan L. An in vivo assessment of the influence of needle gauges on endodontic irrigation flow rate. J Conserv Dent. 2016 March-April; 19(2):189-193]. In order to reach optimal flow rates that produce safe apical pressure and fluid exchange beyond the end of the needle tip, considerable pressures are required on the plunger to compensate for smaller needle gauge diameters [Park E, Shen Y, Khakpour M, Haapasalo M. Apical pressure and extent of irrigant flow beyond the needle tip during positive-pressure irrigation in an in vitro root canal model. J Endod. 2013 April; 39(4):511-515.]. Increased forces on the syringe plunger results in increased pressures within the container leading to subsequent spillage/drippage after applied force due to further expansions of the container materials and residual pressures. Syringes designed to overcome this issue thereby need to maintain a fluid tight seal between the bung and barrel under this greater pressure.
Accordingly, it is desirable to develop a syringe capable of preventing dripping of the fluid from the syringe while also maintaining the fluid seal between the plunger and the barrel.